1. Field of the Invention
The present invention relates to an inspection method for lens products such as a Fresnel lens sheet.
2. Description of the Related Art
In the manufacturing process of a Fresnel lens sheet, a masking material is bonded to the reverse surface of the Fresnel lens sheet (the reverse surface to the surface having formed thereon the Fresnel lens elements), to protect the product during the manufacturing process. And before shipping the product, there is the need to strip off the masking material. In some cases, an antistatic agent or a low-reflection agent is sealed beforehand between the masking material and the reverse surface of the Fresnel lens sheet. In this case, after stripping off the masking material, there is also the need to evenly coat and spread the antistatic agent or the like onto, or over, the entire reverse surface of the Fresnel lens sheet. Further, before shipment, it is necessary to inspect whether or not defects in the lens product exist. As for these defects, there are two kinds of defects. One is a white color defect including a whitish-muddy color of the resin constituting the lens product. The other is a black color defect that results from the entry of foreign substances. Regarding these defects, the presence or absence thereof is determined by separate inspections.
In a conventional inspection method, the following three operations are respectively separately performed. The first operation is the operation for stripping off the masking material. The second operation is the operation for coating the antistatic agent, or the like. And the third operation is the operation for inspecting the above-described two kinds of defects. For this reason, the number of the operation steps that are needed before shipment increases. This lowers the productivity of the lens product and increases the cost thereof.
An object of the present invention is to provide an inspection method that enables the inspection operation, which is needed before shipment, to be performed with a high efficiency, and an inspection apparatus that is used for the execution of the inspection method.
To achieve the above object, there is provided an inspection method for lens products comprising the steps of: placing a sheet-like lens product, a one-side surface thereof having a masking material overlaid thereon, on an operation surface having a black color system of background, with the a masking surface thereof facing up; stripping off the masking material while the lens product is placed on the operation surface and inspecting the lens product through the use of a reflected light; and thereafter inspecting the lens product through the use of a transmission light.
According to the above-described inspection method, the lens product is inspected on the operation surface with a black color system background. The white color defects of the lens product can be easily found with the use of the reflected light from the lens product. In addition, the apparatus is arranged such that the masking material is stripped off on the operation surface. Therefore, after stripping off the masking material, there is no need to newly re-dispose the lens product onto another inspection base in order to inspect of white color defects. Therefore, the operation of stripping off the masking material and the operation of inspecting for white color defects can be simultaneously or continuously performed with high efficiency.
In the above-described inspection method, it is preferable to strip off the masking material while the lens product placed on the operation surface is grounded. By employing such a method, even when the lens product is made of resin, the static electricity that is produced when stripping off the masking material is grounded. Accordingly, no high-voltage static electricity accumulates in the lens product.
The apparatus may be arranged so that, after stripping off the masking material, the inspection based on the use of the reflected light is preformed while a prescribed kind of treating agent is coated onto, and spread over, the entire surface of the lens product. By employing such an inspection, it is possible to inspect the presence or absence of defects while the treating agent is evenly coated onto, and spread over, the entire surface of the lens product, by simultaneously observing the lens product over its entire surface. Accordingly, the operation efficiency is enhanced and it is possible, at the same time, to reliably prevent the missing of an inspection. The treating agent may be of any kind only if it is to be coated on the surface of the lens product. As an example, in case of a resin-made lens product, an antistatic agent may be coated onto the lens product. Such a treating agent may be disposed between the masking material and the lens product, or, may be newly coated onto the lens product after stripping off the masking material.
In the inspection method of the present invention, the lens product may be detached from the operation surface so that the inspection made with transmission light be performed where the lens product is positioned to shade the illumination light with respect to the inspection position. With this inspection, after completing the inspection for white colors defects, it is possible to see the lens product through the illumination light and determine the presence or absence of black colors defects during a series of operations of detaching the lens product from the operation surface and transferring it to another place. Accordingly, it is not necessary to add another independent inspection process to perform only the inspection for black color defects. Resultantly, the efficiency of the inspection operation increases.
On the other hand, in the inspection method of the present invention, the following measures may also be taken. Namely, an inspection base may be prepared that makes selectable a black color system of background and a white color system of background and that can apply the transmission illumination to the white color system of background from inside the inspection base, whereby the background is switched to the black color system to thereby perform a series of operations before the inspection based on the use of the reflected light; and, thereafter, the background is switched to the white color system and the transmission illumination is made from inside the inspection base, whereby the inspection based on the use of the transmission light is performed. In this case, every step from the stripping of the masking material up to the inspection based on the transmission light can be performed using only one inspection base. Accordingly, it is possible to save the space
In the inspection method of the present invention, the inspection based on the use of transmission light preferably is performed from the light-emission surface side of the lens product. By employing such an inspection, it is possible to inspect the lens product from the side where actual observation is made, so that the reliability of the inspection can be enhanced.
An inspection apparatus of the present invention that is usable for the above-described inspection method one that comprises a box-shaped inspection base, on the surface of which there is provided a transparent panel, whereby, at the position inside the inspection base that can be observed through the panel, there is provided a background portion of the black color system.
According to this inspection apparatus looking at the inspection base from its front surface, the background of the panel is colored black. Therefore, with the surface of the inspection base being used as the operation surface, both of the above-described operation of stripping off the masking material and the above-described inspection based on the use of the reflected light can efficiently be performed simultaneously or continuously. Since the panel is transparent, a white-colored transparent background plate is disposed behind the panel, and superposed upon each other. A white color system of transmission illumination is performed from inside the apparatus. By doing so, the inspection based on the transmission light can also be performed on the same operation base.
The background plate may be made to be inserted into and drawn off from behind the panel. By employing such an inspection, with the lens product being kept placed on the surface of the panel, the background plate can be removably attached, with the results of a high level of convenience.
The inspection base may be capable of changing its position in the vertical direction. In this case, the inspection base is vertically moved according to the change in the inspection position. Thereby, the operator can always observe the respective portions of the lens product from the front surface thereof. As a result of this, enhancement in the operation efficiency and the inspection precision can be expected.
The above-described inspection apparatus may comprise a support base which rotatably supports both side portions of the inspection base, the support base including a motor serving as a drive source, a transmission element for distributing the rotating movement of the motor to each side of the inspection base, a feed screw device for converting the rotating movement transmitted by the transmission element into a straight-line movement, and a support member for transmitting the straight-line movement converted by the feed screw device to the inspection base to thereby vertically move the inspection base. If the apparatus is thus constructed, the inspection base can be equally elevated at the left and right sides by utilizing the motor serving as a common drive source, with the result being that the reliability or the stability of the operation is enhanced. The speed at which the operation base is raised or lowered may be made adjustable.
At a lower portion of the panel of the inspection base there may be provided a receiving portion for receiving thereon an object to be inspected; and this receiving portion may be capable of its position being changed in the vertical direction. In this case as well, the vertical position of the lens product can be set to a state where the operation is suitably performed.
Another inspection apparatus of the present invention comprises an operation surface that is equipped with a black color system of background and a receiving portion for receiving thereon a sheet lens product at a lower portion of the operation surface, and a grounded electrically conductive portion is provided on the surface of the receiving portion.
According to this inspection apparatus, the lens product is grounded via the electrically conductive portion. Therefore, even when the operation of exfoliating the masking material bonded to the surface of the resin-made lens product, is performed, which is inevitably followed by the production of static electricity, there is no danger of a high-voltage static electricity accumulating in the lens product.